1. Field of the Invention
The invention relates to an inner heat exchanger for high-pressure refrigerant which is also used as an accumulator or refrigerant collector in an air conditioning circuit. Particularly the inner heat exchanger is used with high-pressure refrigerants such as carbon dioxide or R 134a.
2. Related Technology
Inner heat exchangers are used to enhance the efficiency of air conditioning circuits and are also known as countercurrent supercoolers. By cooling or supercooling the high-pressure flow and superheating the refrigerant vapor, they increase the refrigerating capacity and, therefore, the efficiency of the refrigeration process, which particularly improves the specific refrigeration capacity.
In the state-of-the-art, varied combinations of inner heat exchangers and accumulators are known. In U.S. Pat. No. 4,217,765, for example, an inner heat exchanger and accumulator is disclosed whereby the refrigerant under low pressure collects in the space between a heat exchanger coil and an outer cylinder surface and cools the heat exchanger coil.
From DE 199 03 833 A1 an integrated collector-heat exchanger unit is known that functions as inner heat exchanger and collector/accumulator. The heat exchanger coil used has a helical shape and is in heat contact with the collector space. Also a collector-heat exchanger unit is disclosed that combines a helical coaxial heat exchanger in a collector for the refrigerant.
In DE 14 51 001 a process and a device for the operation of a refrigeration process are disclosed whereby superheating of the refrigerant vapor, with simultaneous supercooling of the high-pressure flow, is taught reflecting the principle of supercooling countercurrent. The heat exchanger and collector disclosed includes various helical tube packages arranged coaxially.
From DE 31 19 440 A1 a plant heat exchanger for refrigeration plants is known that enables a compact structure for the combined heat exchanger and collector function.
All heat exchangers and collectors/accumulators mentioned above have the common disadvantage of not being suitable for use with high-pressure refrigerants. One reason is that the cross-sections of the refrigerant lines are too large. Because of the high pressures in such refrigeration plants, different design principles needed.
This disadvantage is partly overcome by a heat exchanger accumulator shown in U.S. Pat. No. 6,523,365. In U.S. Pat. No. 6,523,365 a device is disclosed that can also be particularly used for high-pressure refrigerants and, to this end, contains microchannels for the high-pressure refrigerant. The flat tubes with the microchannels for the high-pressure refrigerant at high-pressure are arranged helically as a bundle in the upper part of the refrigerant collector/accumulator and are cooled by the refrigerant vapor in the upper part of the case. The refrigerant vapor is led countercurrently in microchannels for the refrigerant vapor, which are arranged parallel to the microchannels for the refrigerant under high pressure.
The heat exchanger/accumulator can partly overcome the disadvantages of the above mentioned state-of-the-art by that the high-pressure refrigerant flow is passed over a heat exchanger coil with microchannels for the high-pressure refrigerant flow. This allows the transfer of heat to refrigerants also at very high pressures. Over the different layers of microchannels, the heat is dissipated to the refrigerant vapor parallel led countercurrently.
The state-of-the-art is still disadvantageous in that heat transfer, however, can only take place in the upper part of the heat exchanger and over a smaller heat transfer surface. Also there are very high flow losses of the refrigerant vapor in the microchannels.
Therefore it is the aim of this invention to provide an inner heat exchanger with accumulator that is suitable for high-pressure refrigerants and is capable of efficiently solving the heat transfer problem. Further, it is intended to realize a simple design solution for the integration of the collector, or accumulator, respectively.